Manuals through 2025 now available!

Our trusted friends have launched a new website named LEMON, which has newer manuals. It also contains all the CHARM manuals.

LEMON is the logical successor to CHARM, I recommend you try it!

Link: lemon-manuals.la

Engine Speed Signal

HEI Wiring Diagram:

The engine speed signal comes from a seven terminal High Energy Ignition (HEI) module in the distributor along CKT 430 (DIST REF). Pulses from the distributor are sent to the PCM where the duration between these pulses are used to calculate engine speed. The PCM adjusts spark advance and sends a signal back to the distributor.